In her first public comments about the row since it emerged that her 12-year-old son, James, is going to the City of London School, Miss Abbott acknowledged that the "agonising" decision would cost her her reputation for political consistency.

But she was prepared to be labelled a hypocrite after shunning the comprehensives in her Hackney constituency in east London if it was in her son's best interests.

Her remarks follow a week of increasingly hostile comments from Labour MPs, with former Left-wing allies accusing her of "double standards".

On BBC2's This Week, Miss Abbott, a member of the Socialist Campaign Group of MPs, said: "I've said very little about this because anything you say just sounds self-serving and hypocritical. You can't defend the indefensible.

Despite the mea culpa, however, Ms Abbott appears to be trying to fight back. She has sold her account of the story to a Sunday newspaper for a sum understood to be equivalent to a term's fees at the £10,000-a-year City of London public school.

In the article, Miss Abbott is expected to justify her actions by claiming that the headteacher at James's primary school warned her off the local comprehensives.

She has told friends she asked the head at Ambler primary school, in Islington, north London, to recommend a local state secondary school for James. According to one friend, the head told her: "I can't recommend any of them".

Miss Abbott, 50, was a vocal critic of Tony Blair's decision to send his sons to a selective state school rather a local Islington comprehensive.

She was equally damning when Harriet Harman, the former Social Security Secretary, did likewise, saying: "She made the Labour Party look as if we do one thing and say another."

In the BBC interview on Thursday night, Miss Abbott said she could not recall having ever criticised Ms Harman's choice.

She went on to say Ms Harman was "one of the first people to ring me" when the story about James's school broke this week. "She said she could not remember [me] saying those things [either].

"I've known Harriet for a long time and she would have remembered if I slagged her off about her son's school."

In fact, research by The Telegraph has found that Miss Abbott did make the attributed remarks during an appearance on Breakfast with Frost in 1996.

James Abbott went on a radio phone-in earlier this week to defend his mother, saying the choice of school was his alone.